1. Field of the Invention
The present invention relates to an improved apparatus for the continuous treatment of webs of textiles and similar materials with a foamed treatment medium.
2. Description of the Prior Art
Methods for the continuous treatment of webs of textile or paper material with a foamed treatment medium are known in the art. See, for example, German Offenlegungsschrift No. 27 22 082. In a method disclosed in this publication, foam is applied directly on a substrate by means of a nozzle. Although it is possible to satisfactorily apply relatively large quantities of a liquid in foam form to a web of material in this manner, such a method is not suitable for the application of small amounts of liquid due to unavoidable variations in the amount of liquid applied by the nozzle on a given surface area of the web, and also local variations in the absorptivity of the web, which cause considerable relative differences in the coverage of the web. This results, when dyeing, in distinctly visible differences in the depth of the color. Also, subsequent wiping or squeezing-off of the foam, as is described in U.S. Pat. No. 2,719,806 for producing coatings, does not provide, according to past experience, sufficient uniformity of application in dyeing operations.
U.S. Pat. No. 2,795,207 discloses a coating apparatus in which a pair of spaced-apart cylinders are disposed parallel to each other at the same height and are adjustable with respect to each other. A web of material is conducted over one cylinder, through the gap between the cylinders, and around the lower part of the second cylinder. In the upper corner between the two cylinders, a foam feeding device dispenses foam into the gap between the two cylinders, so that it makes contact on the one hand with the surface of the second cylinder and on the other hand with the side of the web of material facing the cylinder. The foam is applied at approximately the height of the point at which the web of material is transferred from the first to the second cylinder. The layer of foam remains between the web of material and the second cylinder and is separated from the second cylinder after having travelled through a looping angle of about 180.degree. with the web of material.
The foregoing apparatus is intended to be used for the production of foam rubber coatings on a web of material, where the coating is to be preserved as a layer having its own thickness. Small variations in the feeding of the foam are of no interest in processes effected using this apparatus because they are mechanically compensated for by the subsequent travel around the second cylinder. If such an apparatus were used for dyeing, however, unavoidable local variations in the foam feeding would result in a different coverage of the surface of the web of material with the dyeing liquid, which leads to a non-uniform depth of color. This is particularly so since the foam is applied directly to the web of material and is immediately absorbed by the latter. A non-uniform amount of the dyeing liquid, once absorbed by the web of material by the capillarity between the fibers, or by partial coating of the fibers, cannot be equalized later, contrary to the case of a coating which can be further equalized mechanically and remains as a layer, but should not penetrate into the web of material.
A special problem in the treatment of webs of material of the foregoing type is the uniform application of small amounts of the treatment medium, i.e., the application of just the required amount of treatment medium without the need for dissolving the latter in a large amount of water and to impregnate the web of material therewith, and without having to work with an excessive amount of treatment medium.